The goal of this research is to establish conditions for denaturation, reduction of sulfhydryl bonds, and cleavage of purified thyroxine-binding globulin. These represent the initial steps required to fulfill the overall goal of studying the primary amino-acid sequence of this serum glycoprotein. In addition attempts will be made to acquire crystals of purified thyroxin-binding globulin large enough to permit X-ray diffraction studies in order to obtain information about the tertiary structure of the molecule. These studies are undertaken to understand better the relationship between the structure of thyroxine-binding globulin and its thyroid hormone binding and transport function.